Water-soluble polymeric adhesion promoter and production method

ABSTRACT

A water-soluble polymeric adhesion promoter is represented by the following formula (I):                    
     wherein 
     R is a hydrogen atom, a hydroxyl group or a lower alkyl group having 1 to 4 carbon atoms, and 
     m and k are numbers selected such that m/k is in the range from about 1/0.001 to about 1/0.1, and such that that the polymer (I) has a weight average molecular weight of about 3,000 to about 600,000.

This application is a division of application Ser. No.09/761,194 filedJan. 18 2001, now U.S. Pat. No. 6,455,654.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a water-soluble polymeric adhesionpromoter and methods for its production. In particular, the presentinvention relates to a water-soluble polymeric adhesion promoter usefulfor oxidizable metals such as copper, and to methods for its production.

2. Description of the known art

Numerous polymers have been used to provide coatings and adhesiveness tometals, including alkyd, acrylic, epoxy, polyester and polyurethaneresins. These polymers are required to bond well to the metals and toprovide good coverage, in order to provide corrosion resistance andadhesiveness to the metals.

For this purpose, JP 4-80277A proposes adhesive resins containing abenzotriazole ring in the molecule. The resins may be polyesters,polyurethanes or polyacrylic polymers. However, the benzotriazolering-containing resin of JP 4-80277A is resistant against solvents andwater, and furthermore, is required to be water-insoluble for use inmetal coating technologies. The benzotriazole ring is linked directly tothe polymer chain.

On the other hand, the use of copper has expanded in the semiconductorfabrication industry due to its excellent electrical and thermalproperties. Copper is highly oxidizable and its oxides have a fragilestructure, and thus problems remain to be solved in terms of theprocessability and reliability of the semiconductor fabrication process.The conventional adhesion promoters or corrosion inhibitors employed formetals or ceramics are not suitable for copper or copper products, forexample lead frames made from copper (“copper lead frames”), becausecopper is highly oxidizable and the copper oxides have a weak structure.

Azole compounds or polybenzimidazole (PBI) have been used to inhibitcorrosion of, and provide adhesiveness to, copper metals, in particularcopper lead frames. Azole compounds including benzotriazole (BAT) areadvantageously used because they are water-soluble. However, they havethe disadvantages of poor coverage and poor adhesiveness.

Even though polybenzimidazole (PBI) is advantageous over azole compoundsin terms of coverage and adhesiveness, it still has the problem that itis not soluble in water and thus requires expensive solvents such asdimethylacetamide (DMA). Moreover, DMA causes environmental pollution.

Thus, there has been a need to provide an aqueous adhesion promoterwhich can provide, when it is applied to an oxidizable metal, goodcoverage on the metal surface and excellent adhesiveness for bonding toother materials.

SUMMARY OF THE INVENTION

The present invention provides a new aqueous polymeric adhesion promoterwhich does not have the problems associated with conventional adhesionpromoters or corrosion inhibitors such as benzotriazole ring-containingpolymers, azole compounds or polybenzimidazoles. The present inventionprovides a new polymer useful in inhibiting the corrosion of oxidizablemetals and in providing good adhesiveness to the metals for bonding toother materials.

In accordance with one aspect of the present invention, there isprovided a polymer represented by the following formula (I):

wherein

R is a hydrogen atom, a hydroxyl group or a lower alkyl group having 1to 4 carbon atoms, and

m and k are numbers selected such that m/k is in the range from about1/0.001 to about 1/0.1, and such that that the polymer (I) has a weightaverage molecular weight of about 3,000 to about 600,000.

In particular embodiments, m and k are numbers selected such that thepolymer (I) has a molecular weight of about 30,000 to about 100,000.

The present invention also provides a method for the production of thepolymer of the formula (I) that includes the step of reactingN-(4-phenolyl)-(benzotriazole)amide of the formula

with a polyacryloyl chloride comprising units of the formula

wherein n=m+k.

The present invention also provides an adhesion promoter composition fortreating oxidizable metals, which comprises the polymer of the formula(I) and an aqueous carrier.

The present invention further provides a method for treating the surfaceof an oxidizable metal which comprises the step of applying the polymerof the formula (I) to the surface of the oxidizable metal to provideanti-corrosion and adhesiveness. In particular embodiments, the polymeris applied in the form of an aqueous solution.

The above and other features of the present invention will be apparentto those skilled in the art from the detailed description given below.

DETAILED DESCRIPTION OF THE INVENTION

Priority Korean Patent Application No. 2000-51487, filed Sep. 1, 2000,is incorporated herein in its entirety by reference.

The aqueous polymeric adhesion promoter according to the presentinvention is represented by the following formula (I)

wherein

R is a hydrogen atom, a hydroxyl group or a lower alkyl group having 1to 4 carbon atoms, and

m and k are numbers selected such that m/k is in the range from about1/0.001 to about 1/0.1, and such that that the polymer (I) has a weightaverage molecular weight of about 3,000 to about 600,000.

The polymer (I) provides good coverage, good corrosion inhibition andexcellent adhesiveness when applied to the surface of oxidizable metals.

The polymer (I) can be prepared by following the process indicated inthe reaction scheme (1) given below.

wherein

n=m+k, and

R, m, k and mr/k have the same meanings as defined above in relationwith formula (I).

The polymer (I) can be prepared as follows. Thus, 4-aminophenol ({circlearound (1)}), benzotriazole-5-carboxylic acid (“CBTA” {circle around(2)}) and triphenyl phosphate (“TPP” {circle around (3)}) are reactedtogether to give N-(4-phenolyl)-(benzotriazole-5-carboxyl)amide (“PBCA”{circle around (4)}) and diphenyl phosphate ( {circle around (5)}). Thereaction may be carried out by heating the reaction mixture to about60-160° C. in the presence of base in an organic solvent.

The base can include, but is not limited to, pyridine, ammonia, R′₃N(wherein R′ includes lower alkyl groups having 1-3 carbon atoms) and thelike.

The organic solvents can include, but are not limited to, N-methylpyrrolidone (NMP), dimethyl formamide and the like. TPP ({circle around(3)}) is used in the same or almost equivalent amount as aminophenol ({circle around (1)}), and the organic solvent is used in an excessiveamount, for example about 3 times the amount of aminophenol ({circlearound (1)}).

Then, a polyacryloyl chloride including units having the formula—[CH₂—C(R)COCl—]_(n)— is reacted with PBCA ({circle around (4)}) toobtain the desired polymer,poly(acrylic-co-4-(5-benzotriazole)amidophenyl acrylate) (PAB, (1)).This reaction can be carried out by heating the reaction mixture toabout 20 to about 160° C. in the presence of base in an organic solvent.

The base can include, but is not limited to, pyridine, ammonia, R′₃N(wherein R′ includes lower alkyl groups having 1-3 carbon atoms) and thelike.

The organic solvents can include, but are not limited to, N-methylpyrrolidone, dimethyl formamide and the like.

The equivalent ratio of acryloyl chloride in polyacryloyl chloride toPBCA is determined depending on the desired value of m/k. Thus, theequivalent ratio is the same as the value of m/k.

For the present invention, the weight average molecular weight of thepolymer (I) preferably is about 3,000 to about 600,000 and morepreferably about 30,000 to about 100,000, and is determined by thevalues of m and k. The ratio of m/k preferably is about 1/0.001 to about1/0.1. If the m/k ratio is higher than about 1/0.001, the relativecontent of azole moiety in the polymer (I) is low and the resultingpolymer (I) cannot provide satisfactory adhesiveness. If the m/k ratiois lower than about 1/0.1, the polymer (I) is hardly soluble in anaqueous medium, resulting in a limitation of use.

The ratio between the acid group and the benzotriazole group in thepolymer is important to give proper water-solubility to the polymer (I)and to provide good adhesiveness to the oxidizable metals. The ratiopreferably is between about 1/0.1 and about 1/0.001. In particular, whena metal such as copper is treated with a polymer according to theinvention wherein the ratio of m/k is about 1/0.003, the metal shows anincrease in adhesiveness of about 4 times.

When a composition containing the polymer (I) is applied to the surfaceof oxidizable metals, it gives a good coverage of the metals and themetals show good adhesiveness. The metals can be treated by applying thecomposition by way of dipping the metals in an aqueous solution of thecomposition or spraying the solution on to the metals. That is to say,the polymer (I) is dissolved in water or a water-alcohol mixture in anamount of about 0.05 to about 1 wt % to give an aqueous solution of thepolymer (I). Then, the metals to be treated are dipped into the aqueoussolution at a temperature of about 20 to about 80° C., rinsed with wateror a water-alcohol mixture and then dried at about 20 to about 150° C.Alternatively, the aqueous solution of the polymer (I) is sprayed ontothe metals for about 1 to about 10 seconds and then rinsed and driedsimilarly.

No additive is required to prepare the aqueous solution of the polymer(I). However, surfactants may be used to increase the solubility of thepolymer (I).

The metals to be treated by using the polymer (I) of the presentinvention include, but are not limited to, oxidizable metals, inparticular copper metals. Particularly, lead frames for semiconductorfabrication process can advantageously be treated with the polymer (I).If the lead frames made from oxidizable metals are treated with thepolymer (I) they can keep good adhesiveness and are resistant tocorrosion during several reliability tests under severe and strictconditions of the semiconductor fabrication process. The lead frames canbe made from, but are not limited to, copper metals such as Cu—Fe alloy,Cu—Cr alloy, Cu—Ni—Si alloy or Cu—Sn alloy.

The present invention will be illustrated by way of working examples,which should not be construed as limiting in any way the scope and spritof the invention.

EXAMPLES Example 1

4-Aminophenol (4.07 g, 0.037 mol) and NMP (20 g) were placed in areaction vessel and stirred in 120° C. oil bath. TPP (11.62 g, 0.037mol) in NMP (10 g), CBTA (6.08 g, 0.037 mol) in NMP (33 g), and pyridine(13.42 g, 0.17 mol) in NMP (7 g) were placed in dropping funnels,respectively. Pyridine and TPP were added into the vessel and then CBTAwas added dropwise over a period of 30 min with stirring to give PBCA(5.25 g).

A dry 250 ml 4-neck round bottom flask was fitted with three droppingfunnels and a nitrogen inlet with a magnetic stirrer. Polyacryloylchloride (MW 47,000, 9.60 g (solids 2.40 g)) was placed in the reactionvessel and then PBCA (0.15 g) was added with stirring. Pyridine (0.21 g)was added dropwise for 30 minutes. The reaction proceeded for 2 hr atroom temperature. Distilled water (1 ml) was added to the reactionmixture to hydrolyze the remaining acryloyl chloride. After 2 hr, thereaction mixture was added dropwise to distilled water (440 ml) withstirring and PAB was extracted from the reaction mixture using ethylacetate. The amount of ethyl acetate used was 15 times the amount of NMPused for PAB synthesis. Ethyl acetate was evaporated in a rotaryevaporator and the resulting PAB was dried in a vacuum oven at 50° C. togive the desired poly(acrylic-co-4(5-benzotriazole)amidophenyl acrylate)(MW 50,000; m/k=1/0.02, 1.0 g (yield 40%)).

Example 2

A dry 250 ml 4-neck round bottom flask was fitted with three droppingfunnels and a nitrogen inlet with a magnetic stirrer. Polyacryloylchloride (MW 10,000, 9.60 g (solids 2.40 g)) was placed in the reactionvessel and then PBCA (0.375 g) was added with stirring. Pyridine (0.525g) was added dropwise for 30 minutes. The reaction proceeded for 2 hrsat room temperature. Distilled water (1 ml) was added to the reactionmixture to hydrolyze the remaining acryloyl chloride. After 2 hr, thereaction mixture was added dropwise to distilled water (440 ml) withstirring and PAB was extracted from the reaction mixture using ethylacetate. The amount of ethyl acetate used was 15 times the amount of NMPused for PAB synthesis. Ethyl acetate was evaporated in a rotaryevaporator and the resulting PAD was dried in a vacuum oven at 50° C. togive the desired poly(acrylic-co-4-(5-benzotriazole)amidophenylacrylate) (MW 55,000; m/k=1/0.05, 1.3 g (yield 52%)).

Example 3

A dry 250 ml 4-neck round bottom flask was fitted with three droppingfunnels and a nitrogen inlet with a magnetic stirrer. Polymethacryloylchloride (MW 47,000, 9.60 g (solids 2.40 g)) was placed in the reactionvessel and then PBCA (0.14 g) was added with stirring. Pyridine (0.20 g)was added dropwise for 30 minutes. The reaction proceeded for 2 hr atroom temperature. Distilled water (1 ml) was added to the reactionmixture to hydrolyze the remaining methacryloyl chloride. After 2 hr,the reaction mixture was added dropwise to distilled water (440 ml) withstirring and PAB was extracted from the reaction mixture using ethylacetate. The amount of ethyl acetate used was 15 times the amount of NMPused for PAB synthesis. Ethyl acetate was evaporated in a rotaryevaporator and the resulting PAB was dried in a vacuum oven at 50° C. togive the desired poly(methacrylic-co-4-(5-benzotriazole)amidophenylacrylate) (MW 55,000; m/k=1/0.02, 1.1 g (yield 44%)).

Comparative Example 1

A dry 250 ml 4-neck round bottom flask was fitted with three droppingfunnels and a nitrogen inlet with a magnetic stirrer. Polyacryloylchloride (MW 10,000, 9.60 g (solids 2.40 g)) was placed in the reactionvessel and then PBCA (2.20 g) was added with stirring. Pyridine (3.16 g)was added dropwise for 30 minutes. The reaction proceeded for 2 hr atroom temperature. Distilled water (1 ml) was added to the reactionmixture to hydrolyze the remaining acryloyl chloride. After 2 hrs, thereaction mixture was added dropwise to distilled water (440 ml) withstirring and then stored in a refrigerator for 12 hrs. Then, thereaction mixture was filtered and dried in a vacuum oven at 50° C. togive the desired poly(acrylic-co-4-(5-benzotriazole)amidophenyl acrylate(MW 70,000; m/k=l/0.3, 1.5 g (yield 60%)).

The polymer so obtained is not soluble in water, but soluble in organicsolvents such as dimethyl acetamide or n-methylpyrrolidinone.

Experimental Example 1

Copper coupons (C19400, Poongsan Co., Korea) were degreased withdichloromethane and rinsed with acetone. The copper coupons were thenimmersed in 5 wt % sulfuric acid solution for 5 min to remove the weak,naturally formed copper oxide and rinsed with distilled water. Next, thecopper coupons were immersed in 0.1 wt % aqueous PAB solution(m/k=1/0.05; MW 55,000). The immersion time of the copper coupons in thePAB solution was 15 sec at the reaction temperature of 80° C. Thetreated copper coupons were then taken out, mildly blown with air anddried at 150° C. for 30 min.

Thus treated copper coupons were subjected to a 90° peel test using 5 mmwidth copper strip.

O-cresol Novolac epoxy resin (100 parts) and Nadic methyl anhydride (80parts) as a curing agent were mixed in a 100° C. oil bath, andbenzyldimethylamine (0.3 part) as a catalyst was added to the epoxyresin mixture. The epoxy resin mixture was poured onto copper couponstreated with the inventive adhesion promoter, and then cured at 90° C.for 2 hours and at 150° C. for 4 hours to make the copper/epoxy resinjoints.

After curing the copper/epoxy resin joints, the copper coupons were cutwith the dimensions of 5 mm×70 mm for a 90° peel test. The adhesionstrength of the copper/epoxy resin joints was measured by a 90° peeltest at a peel rate of 5 mm/min using an Instron (Model 4206).

The number of tested specimens was more than 12 for each experimentalcondition. The average peel strength was 380 N/m.

Comparative Experimental Example 1

The same experiments were carried out by following the procedure inExperimental Example 1 except that the step of dipping into the 0.1 wt %aqueous PAB solution was omitted. The average peel strength was 50 N/m.

Comparative Experimental Example 2

The same experiments were carried out by following the procedure inExperimental Example 1 except that a 0.003 M benzotriazole solution wasemployed instead of the 0.1 wt % aqueous PAB solution. The average peelstrength was 160 N/m.

Experimental Example 2

The same experiments were carried out by following the procedure inExperimental Example 1 except that PAB having an m/k value of 1/0.003and a MW of 50,000 was employed. The average peel strength was 250 N/m.

Experimental Example 3

The same experiments were carried out by following the procedure inExperimental Example 1 except that the immersion time of the coppercoupons in the PAB solution was 10 min. The average peel strength was125 N/m.

Whereas particular embodiments of the invention have been describedabove for purposes of illustration, it will be appreciated by thoseskilled in the art that numerous variations of the details may be madewithout departing from the invention as described in the appendedclaims.

What is claimed is:
 1. A process for treating an oxidizable metal toimprove the corrosion resistance thereof and to provide adhesiveness tothe oxidizable metal, the process comprising the step of applying to asurface of said oxidizable metal a water-soluble polymer represented bythe following formula (I)

wherein R is a hydrogen atom, a hydroxyl group or a lower alkyl grouphaving 1 to 4 carbon atoms, and m and k are numbers selected such thatm/k is in the range from about 1/0.001 to about 1/0.1, and such thatthat the polymer (I) has a weight average molecular weight of about3,000 to about 600,000.
 2. A process according to claim 1, wherein saidwater-soluble polymer is apoly(acrylic-co-4-(5-benzotriazole)amidophenyl acrylate).
 3. A processaccording to claim 1, wherein said polymer is applied in the form of anaqueous solution.
 4. A process according to claim 1, wherein saidaqueous solution is prepared by dissolving said polymer in water or awater-alcohol mixture.
 5. A process according to claim 1, wherein saidoxidizable metal is a copper metal.
 6. A process according to claim 3,wherein said oxidizable metal is a copper metal.
 7. A process accordingto claim 4, wherein said oxidizable metal is a copper metal.
 8. Aprocess according to claim 1, wherein said oxidizable metal is selectedfrom the group consisting of Cu—Fe alloy, Cu—Cr alloy, Cu—Ni—Si alloyand Cu—Sn alloy.
 9. A process according to claim 3, wherein saidoxidizable metal is selected from the group consisting of Cu—Fe alloy,Cu—Cr alloy, Cu—Ni—Si alloy and Cu—Sn alloy.
 10. A process according toclaim 4, wherein said oxidizable metal is selected from the groupconsisting of Cu—Fe alloy, Cu—Cr alloy, Cu—Ni—Si alloy and Cu—Sn alloy.11. A process according to claim 1, wherein said oxidizable metal is inthe form of a lead frame.